Abstract

Ammonia borane, , has attracted significant interest as a promising candidate material for hydrogen storage. The effect of pressure on the bonding in was investigated using Raman spectroscopy to over 20 GPa in a diamond anvil cell, and two new transitions were observed at approximately 5 and 12 GPa. Vibrational frequencies for the modes of the proton donor group exhibited negative pressure dependence, which is consistent with the behavior of conventional hydrogen bonds, while the vibrational frequencies of the proton acceptor group showed positive pressure dependence. The observed behavior of these stretching modes supports the presence of dihydrogen bonding at high pressure. In addition, the and bending modes showed an increase in spectral complexity with increasing pressure together with a discontinuity in which suggests rotational disorder in this molecule. These results may provide guidance for understanding and developing improved hydrogen storagematerials.

Received 19 August 2008Accepted 12 November 2008Published online 17 December 2008

Acknowledgments:

This work was supported by the Department of Energy (DOE) under Award No. DE-FG02-07ER46461, the Stanford Institute for Materials and Energy Science under Contract No. DE-AC02-76SF00515, and DOE-NNSA (CDAC). Raman measurements were carried out at HPCAT (Sector 16) of the Advanced Photon Source (APS), Argonne National Laboratory. HPCAT was supported by the DOE-BES, DOE-NNSA, NSF, and the W. M. Keck Foundation. APS was supported by the DOE-BES, under Contract No. DE-AC02-06CH11357.